Chemicals of Life

Chemistry chemicals give cells properties of life must know principles of chemistry to understand biology organisms-bags of chemicals structure determines function Hierarchy chemicalsorganellescellstissuesorgansorganisms

Matter living things are made of matter anything that occupies space & has mass composed of elements

Elements substances which cannot be decomposed into simpler substances by chemical means 92 naturally occurring ones 25 found in living things 96%-H, O, C & N 4%-Ca, P, K & S trace elements-Fe, Mg, Mn (manganese) & I called essential cannot live without them

Periodic Table

Atoms elements are composed of atoms only one kind of atom for each element smallest units of matter that retain the properties of an element

Sub-atomic Particles Protons Electrons Neutrons different elements have different numbers of sub-atomic particles chemical & physical differences of elements are due to these differences

Sub-Atomic Particles Protons Neutrons Electrons one positive charge found in nucleus of atom Neutrons no charge Electrons one negative charge orbit nucleus

Periodic Table atom’s structure determines how element it comprises forms compounds & molecules key to this can be found by knowing number of sub-atomic particles an element possess found in Periodic Table of the Elements

atomic number-number in upper left corner atomic weight or mass number-number located on bottom The mass of any atom is approximately equal to the total number of its protons and neutrons multiplied by the atomic mass unit, u = 1.6605387 10-24 gram.

Atomic Number gives number of protons in an atom Helium has 2 protons

Mass Number found by adding number of neutrons & number of protons He = 4 some atoms of an element may have different mass numbers these are isotopes same number of protons & electrons but different number of neutrons

Number of Electrons net charge of an atom is zero each proton has one positive charge each electron has one negative charge neutrons have no charge to be neural atom must have the same number of electrons and protons atom of helium with 2 protons has 2 electrons

Atomic Number How many protons does Sulfur have? How many electrons? Why?

Chemical Properties arrangement of electrons determines chemical properties of an atom electrons orbit around nucleus found at different energy levels-shells each shell accommodates a specific number of electrons

Electron Shells innermost shell-2 2nd & 3rd-8 number of electrons in outermost shell determines chemical properties of atom those with shells that are not full will interact with other atoms & participate in chemical reactions those with full shells do not interact-inert

Electron Shells H-only one electron in outer most shell C, N, & O very reactive C, N, & O also highly reactive since outer shells are incomplete He-inert or nonreactive because outer shell is full

Reactivity of Chlorine Is Chlorine reactive or not reactive? How can you tell?

Atom Interactions-Chemical Bonds when an atom with an incomplete outer shell reacts with another atom with an incomplete outer shell they can interact or form a bond Share Donate Receive electrons in this way both atoms can have a completed outer shell

Types of Chemical Bonds Covalent Bonds share electrons Ionic give or receive electrons

Sodium & Chloride

Ionic Bonding

Covalent Bonds 2 atoms with incomplete shells each share a couple electrons so at any one time one atom has a completed outer shell forms molecules

In Class Exercise Pretend you are an atom Take the number of your birth month as your atomic number Determine the configuration of electrons in your valence shell Find another atom that you might interact with to form ions or new molecules Demonstrate-draw on the board

Chemical Reactions elements combine to make molecules & compounds 2 H2 + O2  2H2O 2 molecules of H react with one molecule of O (reactants) to form 2 molecules of water (product) arrow indicates direction of reaction two sides of equation on either side of arrow must balance

Water single most important constituent of body life on Earth depends on unusual structure & nature of water Organisms consist mostly of water-2/3rds total body weight of humans.

Importance of Water Organisms consist mostly of water 2/3rds total body weight of humans Biochemistry is a wet chemistry biological molecules do not react chemically unless in solution Water is an important reactant nearly all chemical reactions in the body occur in water Foods are digested to their building blocks by decomposition reactions called hydrolysis involves addition of water When large molecules form from smaller ones, water is removed in dehydration synthesis or condensation reactions

Water Structure 2 H atoms attached covalently to one O2 molecule sharing of electrons is not equal oxygen pulls more on electrons than does hydrogen electrons spend more time near oxygen than hydrogen unequal sharing produces- polar bond Nonpolar bond bonds in which two atoms involved have an equal pull on electrons

Water Structure O2 attracts electrons more strongly than H-giving water an asymmetrical distribution of charge result-V-shape H end has positive charge Oxygen end has negative charge water has 2 poles-polar polarity results in weak electrical attractions between neighboring water molecules

Polarity of Water Polarity results in weak electrical attraction between neighboring water molecules slightly positive Hs in one water molecule attract slightly negatively charged O2 in another water molecule opposite electrical charges attract water molecules attract each othermaking water kind of sticky these weak attractions-hydrogen bonds much weaker than covalent or ionic bonds

Polarity, H Bonding & Water’s Properties cohesive nature ability to moderate temperature ice floating universal solvent properties Cohesive Nature-water molecules attract eachclump together -cling or stick together to form films-surface tension. Water beads up into spheres when on hard surface. Important in living world-tress depend on this to help transport water from roots to leaves. Moderation of Temperature-High Heat Capacity-heat absorption-ability to absorb and retain heat. H bonding allows water to resist temperature changes. Temperature and heat-related-but different. Heat-amount of energy associated with movement of atoms and molecules in body of matter. Temperature-measure of intensity of heat-average speed of molecules rather than total amount of heat energy in body of matter. Example-swimmer in large body of water-may have higher temperature than water; water has more heat because of its immense volume. Heatwaterheat energy first disrupts H bonds-makes molecules move faster. Because heat first used to break bonds and not raise temperaturewater absorbs large amount of heat while only warming few degrees. Water has high specific heat index-can absorb lot of heat before begins to get hot. Why water is valuable to industries and in car radiators as coolant. High Heat of Vaporization-temperatures must be quite high before individual molecules have enough energy to break free and become water vapor-gaseous. Carries heat away with it as transforms from liquid to gas-cooling effect of perspiration-evaporative cooling. When substance evaporates-surface of liquid-what is remaining behind cools. Occurs because molecules with greatest energy-hottest ones-vaporize first. Globally-surface evaporation cools tropical oceans. Individually-prevents over heating. When water coolsremains liquid over wide range of temperatures-H bonds formreleases heat-water releases large amount of heat to surroundings while water temperature only drops few degrees. Freezing and boiling points far apart-freezes-32o F and boils-212o F. Unusually large amount of heat energy needed to change temperature of 1 gram of water by 1oC-once amount of water has reached particular temperature-changes temperatures only very slowly-thermal inertia-helps stabilize body temperatures. Large body of water can store huge amount of heat from sun. In coldheat given off from gradually cooling water can warm air-stabilizes ocean temperatures. Ice Floating-when most liquids cool molecules get closer and closerif cold enoughsolid. When water molecules coolmove apartice. Ice has fewer molecules than equal volume of liquid water less densefloats. Due to H bonding. H bonding lasts longer in ice; with each molecule bound to 4 neighbors. Ice is spacious crystal. Promotes life because if water behaved as other liquidsall water would freeze solid. When warming only upper few inches would thaw. When deep body of water coolsfloating ice insulates liquid water beneathlife persists. Universal Solvent-if substance dissolves in water-soluble-forms solution-uniform mixture of 2 or more substances. Solvent-medium in which other atoms, molecules or ions are dispersed. Dispersed substances-solutes. Water-powerful solvent-universal-dissolves more substances than any other liquid. Solution formed-aqueous solution. Fluids of lifeaqueous. Being soluble in water means that wherever water goes, through ground or through body-takes along with it chemicals, minerals, and nutrients. Useful as transport mechanism. Because of polar nature-water molecules orient themselves with slightly negative ends towards positive side of solutes and vice versa-first attracting and then surrounding them. Compounds formed by ionic bonds-ionize or dissociate-in water-broken as individual ions interact with either positive or negative end of water. Producing cations (+) and anions (-) surrounded by water molecules forming hydration sphere. Aqueous solution with anions and cations conducts electrical currents. Cations move to negative side having + change and anions move to positive side having– charge. Electrical forces across cells affects functioning of cells-muscle contraction and nerve function. Soluble inorganic molecules whose ions will conduct an electrical current in solution- electrolytes. NaCl-electrolyte. NaCl + H2ONa+ + Cl-. Changes in body fluid concentrations of electrolytes disturbs almost all vital functions. Decrease in K+ muscle paralysis; increaseweak, irregular heartbeats. Organic molecules have polar covalent bonds-attract water. Hydration shells form around large charged molecules-proteins-shielding them from effects of other charged substances and preventing them from settling out of solution. Hydration spheres carry them into solution. These mixtures are colloids-solutions of dispersed proteins or other large molecules which do not come out of solution-Jello. Particles remain in solution indefinitely. Suspension-contains even larger molecules that will if undisturbed settle out of solution due to gravity. Stirring sand in watersuspension lasts until sand settles bottom. Molecules that dissolve in water are hydrophilic-water loving-those that do not readily react with water-hydrophobic-have few if any polar, covalent bonds. These are non polar-when exposed to water-hydration spheres do not formmolecules do not dissolve. Body fat-large, insoluble droplets of hydrophobic molecules trapped in watery interior of cells.

Dissociation compounds formed by ionic bonds will ionize or dissociate in water dissociation produces cations (+) & anions (-) aqueous solution containing anions & cations will conduct electrical currents cations move to negative side having a + change & anions move to positive side having a – charge soluble inorganic molecules whose ions will conduct an electrical current in solution are called electrolytes NaCl is an electrolyte NaCl + H2ONa+ + Cl-

Acids H+ & OH- are in solutions at all times H2O <-------> H+ + OH- -reversible reaction some compounds add more hydrogen ions others remove them compound that donates hydrogen ion-acid HClH+ + Cl- acidic solution is one that has more H+ than OH-

Bases compound that accepts or removes hydrogen ions is a base NaOHNa+ +OH- basic solution- has more OH- than H+

pH scale pH = potential hydrogen scale developed in 1909 by Dane Soren Sorensen beer brewer looking for a way to check acidity of beer describes how acidic or basic a solution is scale ranges from 0-14 0 = most acidic 14 = most basic 7=neutral

pH at neutral pH H+ = OH- pH < 7 is acidic pH > than 7 is more basic or alkaline

Buffers pH of blood ranges between 7.35-7.45 value must be maintained in narrow range even small change can lead to severe metabolic consequences biological fluids contain buffers substances that resist changes in pH by accepting H+ when in excess & donating H+ when depleted